TAMR is expected to be one of the future generations of magnetic recording technologies that will enable recording at ˜1-10 Tb/in2 data densities. TAMR involves raising the temperature of a small region of the magnetic medium to near its Curie temperature where both of its coercivity and anisotropy are significantly reduced and magnetic writing becomes easier to achieve even with weak write fields characteristic of small write heads in high recording density schemes. In TAMR, optical power from a light source is converted into localized heating in a recording medium during a write process to temporarily reduce the field needed to switch the magnetizations of the medium grains. Thus, with a sharp temperature gradient of TAMR acting alone or in combination with a high magnetic field gradient, data storage density can be further improved with respect to current state of the art recording technology.
In addition to the components of conventional write heads, a TAMR head also typically includes an optical wave guide (WG) and a plasmon antenna (PA) or plasmon generator (PG). The wave guide serves as an intermediate path to guide the external laser light to the PA or PG where the light optical mode couples to the local plasmon mode of the PA or to the propagating plasmon mode of the PG. After the optical energy is transformed to plasmon energy, either with local plasmon excitation in the PA or with energy transmission along the PG, it is concentrated at the medium location where heating is desired. Ideally, the heating spot is correctly aligned with the magnetic field from the write head to realize optimum TAMR performance. However, in current TAMR configurations, alignment has been difficult to achieve and there is need for improvement in order to compete with other forms of magnetic recording such as microwave assisting magnetic recording (MAMR).
A thermally assisted magnetic head structure disclosed in U.S. Patent Application Publication 2010/0103553 employs an edge plasmon mode that is coupled to a wave guide as represented in FIG. 1a. Conventional components of a magnetic recording structure include a main pole 1, return pole 3, and write coils 5 formed along an air bearing surface (ABS) 8-8. In the ABS view, plasmon generator 2 has a triangular shape with an edge proximate to the waveguide 4. As shown in the cross-sectional view, waveguide (WG) 4 directs the input optical light wave 6 toward the ABS 8-8 and is recessed a certain distance from the ABS. Optical wave 6 couples to the edge plasmon (EP) mode 7 that is excited and propagates along the sharp edge 9 of plasmon generator 2 adjacent to the WG 4. Plasmon mode 7 further delivers the optical power toward the ABS and locally heats a medium (not shown) placed underneath the plasmon generator 2. A plasmon generator is typically made of noble metals such as Ag and Au that are known to be excellent generators of optically driven surface plasmon modes. The local confinement of the edge plasmon mode 7 is determined by the angle and radius of the triangle corner.
In theory, an edge plasmon generator (EPG) can be engineered to achieve a very tiny light spot as well as a high temperature gradient in the medium for a TAMR recording scheme. Moreover, a plasmon generator with a substantial length in a direction perpendicular to the ABS will have a large metal volume that can avoid localized heating damage during TAMR writing compared to an isolated plasmon antenna of smaller volume. In TAMR, a written bit strongly depends on the thermal spot size and shape in the recording layer, and on the alignment between the magnetic gradient and thermal gradient. The magnetic medium is heated by an EPG in which the optical energy is confined around a vertex (tip) of two converging EPG sides thereby forming a so-called edge plasmon mode. Clearly, the confinement of the optical spot or EP mode in this design is a function of the shape, angle, and size of the tip, the metal composition of the EPG, and the dielectric material surrounding the tip.
In the prior art, the objective of correctly aligning the optical heating profile with the magnetic field profile has not been adequately addressed. As FIG. 1b illustrates, state of the art TAMR technology still delivers the heating spot represented by heating profile 9 at the far leading edge of the main pole's magnetic field profile 12. Although this configuration can achieve writing when sufficient heating is applied, it is not the most desired condition for TAMR writing. The full advantage of TAMR recording can be realized when the heating profile 9 slope is aligned at the same y-axis (down-track) position as the slope 10 or 11 of the magnetic trailing edge field. As a result, magnetic and thermal gradients assist each other to achieve the highest effective gradient during magnetic recording. Due to structural waveguide limitations such as thickness and configuration, and the choice of antenna design, a highly effective alignment of magnetic and thermal gradients has not been fabricated yet in TAMR technology. In addition to the issue of down-track mis-alignment as mentioned above, cross-track alignment is also affected by the overlay of the antenna heating spot on the highest head field. Thus, there is a need for a better plasmon antenna design and an optimized TAMR structure so that the alignment of the heating spot and magnetic field is improved during a write process without sacrificing the efficiency of coupling the optical energy into the plasmon mode.
In U.S. Patent Application 2010/0128376, a nearfield light generator is described that applies nearfield light to a minimal area.
U.S. Pat. No. 7,710,686 teaches a nano aperture antenna having a small spot diameter of tens of nanometers.